Physiology 3120 Study Guide - Midterm Guide: Enteric Nervous System, Motility, Gastrointestinal Tract

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Published on 26 Nov 2011
Human Physiology
Wednesday, March 31, 2010
“Gastrointestinal VI”
Gastric Motility (cont’d)
The tracing shown last class deals with slow waves only; doesn’t deal with mechanical activity; need to
induce APs at the blips to produce mechanical activity; orientation of slow waves dictates the sequence
of contractile waves (wave of propulsion is a result of sequential contractions at progressively distal
gastric segments)
If you make cuts between the segments, each segment goes to its own intrinsic frequency, with the
most proximal part having the highest frequency; in an intact stomach, the frequencies are the same, but
the most proximal part of the stomach is the most dominant oscillator (i.e. the pacemaker); the
importance of this property is to ensure a wave of contraction to push stuff into the intestine, and a
system that moves material faster as you move towards the pylorus
Vagus has very few branches to the stomach
Vagal information stimulates the enteric nervous system, which projects to smooth muscle, as
well as secretory cells; placing a balloon into the stomach and inflating it will cause motility
because it activates stretch receptors, which activates the ENS to release ACh, which works on
the slow wave to induce mechanical activity
Gastric Emptying
Absorptive and digestion capacity of the duodenum is limited; so don’t want to overwhelm it by
pumping all the material into the duodenum at once; want to regulate how quickly food gets from distal
stomach to duodenum; not to mention the acidity of the stomach fluid that must be neutralized by the
Can either increase or decrease the rate of emptying
Increase rate
Increase volume
Decrease rate
Increase acidity
Increase fat
Increase protein
Increase carbohydrates
The body detects the osmolar load of these compounds using chemoreceptors/osmoreceptors
How to change the rate (i.e. what actually happens)?
Fluid moves in response to a pressure gradient
Modulate the contraction of smooth muscle to control the rate of emptying (not the pyloric
sphincter); to increase rate, you can increase the number OR amplitude of contractions in the
distal stomach relative to the duodenum; to decrease rate, increase the number OR amplitude of
contractions in the duodenum; the manipulation is only designed to change the orientation of the
pressure gradient
Acid chemoreceptor activates smooth muscle cell via ENS; also goes to the chief cell (which
secretes secretin); note that although the ENS in the duodenum would activate the ENS in the
stomach (because the ENS is a network), there will be a latency
Esophageal Motility
Characteristics shared with stomach
Mechanical activity is garden-variety peristalsis
No slow wave, just like proximal stomach
The upper 1/3 is skeletal muscle/cricopharyngeus muscle (i.e. not all smooth muscle); the importance of
this has to do with the upper esophageal sphincter (UES); an anatomical (can see it) and functional
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